The invention relates to a rotary pump
In particular, the invention is concerned with a rotary pump, which is installed at the machine bed of a machine tool and is used to pump out cooling liquid for the machine tool, which has collected in the liquid basin in the machine bed, so that it can be supplied once again to the tool, optionally with the help of a further pump. Rotary pumps, having a radial construction with open impeller vanes have proven to be particularly suitable for this application, since they are relatively insusceptible to particles, such as chips and the like, which are suspended in the cooling liquid. The rotary pump is disposed in the liquid basin with a vertically oriented axis of rotation of the impeller and a downward pointing intake opening, which is approximately at the level of the liquid. Usually, the pump is designed so that its pumping output is somewhat greater than the inflow of cooling liquid into the liquid basin. When the level of the liquid reaches that of the intake opening, the pump therefore works in a slurping operation, so that a certain amount of air is also aspirated and the liquid pumping output decreases. In this way, the liquid level is control automatically to the level of the intake opening.
In recent years, emulsions, which contaminate the environment relatively little because of their special composition, have been used increasingly as cooling liquid for machine tools. Oil is also used to an increasing extent as cooling liquid for high-performance machine tools. Modem emulsions and the oil, used as cooling liquid, are not degassed as readily as the cooling liquids used in the past. The cooling liquid, which is pumped from the machine bed to the tool or to the workpiece and subsequently collected and returned once again in a closed cycle to the liquid basin in the machine bed, frequently comes into contact with air during this recycling and is mixed with air, especially in the slurping operation of the pump and the concentration of air in the liquid in the form of a dispersion of finely divided air bubbles, increases. In the rotary pump, the aspirated mixture of cooling liquid and air is separated by centrifugal forces. The heavier liquid is forced radially to the outside and an air cushion is formed in the inner region of the pump chamber in the vicinity of the axle of the impeller, becomes larger as the operating time increases and, when it has reached at appropriate size, interferes with the inflow of cooling liquid through the intake opening.
From the DE 43 25 549, a rotary pump of the introductory portion of claim 1 is known, for which at least one venting channel extends approximately from the position of the inner ends of the vanes of a radial impeller along the wall of the intake connecting piece up to the level of the intake opening of the intake connecting piece. The venting channels lead from the inner region of the pump chamber to the open lower end of the intake connecting piece. For this pump, the liquid or the mixture of liquid and air is pumped axially into the inner region of the pump chamber by an axial impeller in the intake connecting piece, as soon as the liquid level is above the intake opening at the lower inlet end of the intake connecting piece. Because the axis of rotation of the impeller is vertical and the intake connecting piece dips in to the liquid basin, this pump makes possible a space-saving construction with a vertical arrangement of the motor above the pump and a reliable decrease in the air cushion in the pump chamber is ensured without an additional exhaust fan.